Question

The standard molar enthalpies of formation of cyclohexane (l) and benzene (l) at `25^(@)C` are `-156` and `+49 kJ mol^(-1)`, respectively. The standard enthaly of hydrogenation of cyclohenxene (l) at `25^(@)C` is `-119 kJ mol^(-1)` Use this data to estimate the magnitude of the resonance enegry of benzene.
A. `152 kJ mol^(-1)`
B. `-240 kJ mol^(-1)`
C. `-152 kJ mol^(-1)`
D. `240 kJ mol^(-1)`

Answer 1

Correct Answer - C
`6C + 6H_(2) rarr C_(6) H_(12) , -156` ....(1)
`6C + 3H_(2) rarr C_(6)H_(6) , + 49`...(2)
`C_(6) H_(10) + H_(2) rarr C_(6)H_(12) , -119`
`rArr C_(6)H_(6) + 3H_(2) rarr C_(6) H_(12) , -119 xx 3`...(3) ltbr. [Obseved ]from (1) and (2)
`C_(6)H_(6) + 3H_(2) rarr C_(6) H_(12) -205` [Calculated]
`,.` Reasonance energy `= (Delta H)_("obs") ~ (Delta H)_("cal")`